It is well known that the electrical properties of teeth change when disease or decay alters the physical composition or structure of the affected teeth. In the past, it has been found that measurement of the change in electrical properties; for example, the resistivity or conductivity of the tooth, provides a rapid, simple and effective means of detecting disease or decay without the difficulties associated with present mechanical probing techniques.
The method of diagnosing caries by measuring electrical resistance was first proposed by Pincus (1951), using DC currents of up to 300 microamps. Mayuzumi, Suzuki and Sunada (1964) extensively studied the electrical resistance and the degree of dental caries and caries susceptibility, and concluded that teeth, having a low electrical resistance, had a high susceptibility to dental caries. The potential applied to the tooth was less than 1 volt AC, and teeth showing electrical resistance of over 600 K had no caries and had low caries susceptibility, whereas teeth with resistance of under 250 K had actual dentinal caries, or most of such teeth suffered caries sooner or later, regardless of sound appearance of pits and fissures of those teeth. Thus, by the measurement of conductivity, it is possible to detect in a meaningful manner whether or not teeth are caries-free or alternatively to detect the existence of early incipient caries, late incipient caries and carious lesions of teeth (see, for example, Japanese Patent No. 280,012).
However, despite the knowledge concerning the detection of caries employing an electrical caries detector, a simple portable instrument has not been developed for the reliable measurement of dental caries employing measurable change in electrical properties of the tooth, such as by the measurement of the electrical resistance or conductivity of the tooth from a prope tip through the dental pulp to a ground.
One difficulty associated with past proposed dental-caries detectors has been the wide variation in electrical-property measurements obtained by the instruments. It has been found that conductivity measurements made on a wet tooth are often not very stable, and such measurements have been suspected of giving false positive values. The presence of a condutive liquid in a deep carious lesion is required during a measurement by a dental-caries detector, to insure good electrical conduct between the probe tip by which the current is applied to the tooth, and which is placed or fixed on the tooth surface and the lesion located well below the tip and within the tooth. There exists a need for a simple, portable, electrical, dental-caries detector which will provide statistically meaningful, reliable and consistent electrical-property measurements and which will overcome the varying and false measurements associated with past detectors.